Suction dredger and method of suction dredging

ABSTRACT

METHOD AND APPARATUS FOR SUCTION DREDGING PARTICULATE MATERIAL SUCH AS SAND. A SUCTION PIPE IS INSERTED INTO A BODY OF SAND BELOW THE BOTTOM OF A BODY OF WATER TO WITHDRAW A WATER-SAND SUSPENSION HAVING A DESIRED CONCENTRATION OF SAND IN SUCH SUSPENSION. AT THE LOWER END OF THE PIPE, THE SAND IS DRAWN IN AT VERY HIGH CONCENTRATION AND AT SOME LEVEL ABOVE THIS POINT WATER IS SEPARATELY IN-   TRODUCED AND THE DESIRED CONCENTRATION IS OBTAINED BY ADJUSTING THE LEVEL AT WHICH THE WATER IS INTRODUCED. THE CONCENTRATION OF THE RESULTING SUSPENSION IS MEASURED TO ENABLE THE LEVEL OF WATER INTRODUCTION TO BE ADJUSTED PROPERLY.

Oct. 12, 1971 JAN DE KONING 3,611,595

SUCTION DREDGER AND METHOD OF SUCTION DREDGING Filed Aug. 8, 1969 2Sheets-Sheet 1 INVENTOR ae KONiNG ATTORNEYS 0d. 12, 1971 JAN 35 KONING3,611,595

SUCTION DREDGER AND METHOD OF SUCTION DREDGING Filed Aug. 8, 1969 2Sheets-Sheet 2 FIG. 6.

mvsmon JAN de KONING United States Patent Ofice 3,6ll,595 Patented Oct.12, 111971 3,611,595 SUCTION DREDGER AND METHOD OF SUCTION DREDGING Jande Koning, Amsterdam, Netherlands, assignor to N.V. Ingenieursbureauvoor Systemen en Octrooien Spanstaal, Rotterdam, NetherlandsContinuation-impart of application Ser. No. 524,934, Feb. 3, 1966. Thisapplication Aug. 8, 1969, Ser. No. 866,050 Claims priority, applicationNetherlands, Feb. 4, 1965, 6501404 Int. Cl. E02f 3/92 US. C]. 37-58 11Claims ABSTRACT OF THE DISCLOSURE Method and apparatus for suctiondredging particulate material such as sand. A suction pipe is insertedinto a body of sand below the bottom of a body of water to withdraw awater-sand suspension having a desired concentration of sand in suchsuspension. At the lower end of the pipe, the sand is drawn in at veryhigh concentration and at some level above this point water isseparately introduced and the desired concentration is obtained byadjusting the level at which the water is introduced. The concentrationof the resulting suspension is measured to enable the level of waterintroduction to be adjusted properly.

CROSS REFERENCE TO RELATED APPLICATION This application is acontinuation-in-part of application Ser. No. 524,934, filed Feb. 3,1966, now abandoned.

SUMMARY OF THE INVENTION This invention relates to a suction dredgerinstallation comprising a pump and a suction pipe which is connected tothe pump and which has at least one first suction nozzle at the end andat least one second suction nozzle between the pump and the end. Theinvention also relates to a method of sucking up spoil by means of thesaid suction dredger installation, wherein the first suction nozzledraws spoil and the second suction nozzle draws mainly water into thesuction pipe.

A suction dredger of this kind and a method of this kind are disclosedin German patent specification 815,625. This specification proposes soto construct the end of the suction pipe that the second suction nozzlecan draw a considerable amount of water, more particularly if the firstsuction nozzle becomes clogged by large objects, i.e., large stones orrocks. In the known method, the first suction nozzle is held above thecavity while the attempt is made to obtain a constant spoilconcentration in the drawn-up suspension. With the known method it isvery difiicult to obtain this constant concentration because thecondition in front of the first suction nozzle are continuously subjectto considerable variation.

The invention provides a method and a suction dredger installation ofthe type specified in the first paragraph, with considerable advantagesover the prior art.

In the method according to the invention, the end of the suction pipe isinserted into the cavity and the distance between the two suctionnozzles is adjusted to control the concentration of spoil in thedrawn-in suspension in dependence upon the column of spoil and any othermaterial fioating thereon above the first suction nozzle. The spoilconcentration in the sucked up suspension is thus accurately adjusted tothe required value.

An important advantage of the method according to the invention is thatit can be used to draw spoil from the cavity even beneath an impure toplayer, for example a layer of clay. The impurities and large objects atthe bottom of a dredging site cannot ClOg the suction nozzles with themethod according to the invention. Preferably, the end of the suctionpipe is inserted deeply into the cavity so as to reduce the risk of theimpure top layer reaching the suction nozzle. Drawing spoil from a deepposition beneath the cavity does not require more power than drawingspoil at the surface of the cavity.

The invention also provides a suction dredger installation adapted moreparticularly to performing the method according to the invention andwhich is characterized by adjustability of the distance between the twosuction nozzles.

Finally, the invention provides a number of advantageous constructionsof the suction pipe end, the distance between the two suction nozzlesbeing adjustable, while the position of the first suction nozzle and thesuction pipe with respect to the hard cavity can be maintained.

The invention will be explained hereinafter with reference to a methodand a number of suction pipes for the suction dredger installationaccording to the invention.

BRIEF DESCRIPTION OF THE FIGURES OF DRAWINGS FIG. 1 is a diagrammaticview of the surroundings of the end of a suction pipe during performanceof the method according to the invention.

FIGS. 2, 3 and 4 each show an end of a suction pipe for a suctiondredger installation according to the inven tion.

FIG. 5 is a detail corresponding with detail V of FIG. 4, of anothermodification of the end of the suction pipe for a suction dredgerinstallation according to the invention.

FIG. 6 is a diagrammatic View illustrating the component parts of thesuction dredger installation according to the present invention.

With reference to FIG. 6, certain relationships according to the presentinvention will be readily discernible therefrom. As shown, the suctiondredger installation includes a suitable pump 20 having a discharge line21 from which a fluid suspension of water and sand is obtained. It willbe understood that the suction dredger installation may be mounted, forexample, on a barge or the like with the barge receiving the materialdischarged.

The inlet side of the pump is connected to the conduit system indicatedby the reference character 22 which leads to the suction pipe 23 which,at its lower end as will hereinafter be more particularly pointed out,is adapted to withdraw the spoil or sand into the conduit system. As isalso pointed out hereinafter, a separate inlet for water is providedinto the conduit system and the level at which the separately introducedwater is comingled with the suspension of an inherently high sandconcentration is controlled to produce the desired and much lower sandconcentration reaching the discharge line 21. The control for adjustingthe point of water introduction is indicated by the reference character24 and may take any suitable form compatible with the mechanism actuallyutilized for adjusting the water level intake.

Additionally, a sand concentration meter 25 is provided which measuresthe concentration of sand in the conduit system as effected by thecomingling of the high sand concentration introduced into the lower endof the suction pipe and the separately introduced water. This meter maybe of any suitable type, as for example to US. Pat. 2,661,550 or2,768,529.

In any event, it is desired that the concentration of sand in thesuspension be maintained in the range of about 10 to about 25%. Withinthis range, good pumping efi"1 ciency is obtained while at the same timeeffecting an efficient and essentially continuous withdrawal of sand orspoil from the bed of material being dredged.

In the method according to the invention, the suction dredgerinstallation used has a suction pipe whose end dilfers from conventionalconstructions. Thus, the figures show only the free part of the suctionpipe of the suction dredger installation which comprises a spoil pumpbetween a pressure pipe and a suction pipe.

The suction pipe 3, which is shown in the operative position in FIG. 1,comprises a first suction nozzle 1 and a second suction nozzle formed byopening one of the apertures 211-2p. These apertures are at differentdistances from suction nozzle 1 and normally each one is closed by aslide 4. Each slide 4 can be remotely adjusted independently by suitablemeans, i.e., hydraulic means, between two positions in which the openingis respectively open and closed.

The suction pipe 3 is continuously moved in the direction of arrow 5 inthe inclined position shown in FIG. 1. FIG. 1 also shows the followingin the upward direction: a layer of sand 6, a layer of clay 7,impurities, i.e. wood, 8, resting on the layer of clay, and water 9. Thesoil enclosed by line is brought into suspension by undermining whileoutside the line 10 the soil is consolidated.

According to the invention, aperture 2m is left open so that at thataperture the incoming water and the suspension drawn through the firstaperture 1 are mixed with a very high sand concentration. Thehigh-concentration suspension rises automatically to the level of theaperture 2m in the suction pipe because the end of the suction pipeforms a communicating vessel with the cavity in the consolidated soilindicated by line 10. It will be immediately apparent that if aperture 2for example, were opened, the suspension would run out of the suctionpipe into the water. The water would thus be prevented from enteringthrough such aperture, so that the pump would draw only spoil with avery high concentration. This would result in stalling of the pump andsand clogging of the suction pipe, pump and/or pressure pipe.

On the other hand, if, for example, aperture 2 were opened, the waterentering through that aperture would tend rather to be drawn in than thehigh-concentration suspension which would first be drawn in fromaperture 2m to aperture 2p by the pump suction. The result would be asuspension having a too low sand concentration. In addition, the factthat a column of heavy suspension is drawn to an unnecessary heightmeans a loss of pumping power.

By opening the correct aperture of the apertures 2a-2p the sandconcentration in the suspension can be controlled and the pumping powercan be applied with maximum economy.

Sand is preferably drawn deeply from the cavity. This greatly reducesany chance of impurities or clay being drawn in. With the methodaccording to the invention, in view of the frictional resistance in thebottom part of the suction pipe the fact that sand is drawn in from alow level does not require more energy than if it were drawn from thelevel of the impurities 8. With the method according to the inventionthe dredged well is not first freed of clay and impurities; instead, theweight of clay and impurities is put to advantage for drawing in thesand. Neither the drawing of sand to the aperture 2m nor the conveyingof water to the suction pipe 3 requires energy.

In order to prevent sand entering the second suction nozzle instead ofwater if the cavity suddenly falls in, a water pipe 111 is preferablydisposed around the suction pipe 103, the water pipe being closed at thebottom and open at the top, see FIG. 2. This water pipe always providescommunication between the open second suction nozzle 102a-102p, and thewater above the dredging site. Otherwise, the construction and operationof the suction pipe of FIG. 2 in the same as that of the suction pipe ofFIG. 1.

The pressure difference acting on the sand at the sand inlet and causingit to flow upwardly is determined by the weight of the column h of sand,clay and impurities above the first section nozzle 1. This pressuredifference is cancelled out by adjusting the second suction nozzle 2 toapproximately the level of the top of the column 11. Adjustment of thesecond suction nozzle to a higher or lower level respectively results inmore water and more sand being pumped up. The concentration of sand inthe suspension can be accurately controlled by continuous variation ofthe distance between the first and second suction nozzles.

FIG. 3 shows a suction pipe 203 with a continuously variable distancebetween the first suction nozzle 201 and the second suction nozzle 202.In FIG. 3, the second suction nozzle 202 is formed by one or more slotsin the suction pipe completely closed by means of slide 204 engagingaround the suction pipe 203. This slide is remotely adjustable by ahydraulic cylinder provided between the water pipe 211 and the slide204. The level of the second suction nozzle is determined by the levelof the bottom end of the slide 204.

The suction nozzle 303 shown in FIG. 4 is substantially the same as thatshown in FIG. 3. For a proper understanding of the suction pipe 303according to FIG. 4, it should be noted that the suction pipe 303consists of four parts, i.e., a pipe part 303a rigidly connected to thepump, a part 3031) axially slidable with respect to the fixed part 303a,a part 303a having a larger diameter and integral with the pipe 311disposed around the suction pipe 303 and a pipe part 303d having a samediameter as pipe part 303b and being connected by means of a basket 304to the end of the pipe part 303a. Thereby two first nozzles 301a and30112 are provided in the lower end of the pipe parts 303d and 3030respectively, while the water inlet is formed by an annular gap betweenthe water pipe 311 and the bottom end of the slidable part 3033b. Thelatter part is guided by three wheels, 313, which are distributed overthe periphery, with respect to the water pipe 311 secured to the fixedpart 303a.

The part 3031: is adjusted by means of three hydraulic cylinders 312distributed over the periphery.

Preferably, adjustment of the distance between the first nozzle 30111and the water inlet is obtained automatically. The means for operatingthe slides, or valves, 4 and/or the slidable part 303b can be controlledby the concentration meter incorporated in the suction pipe or pressurepipe.

While the end of the suction pipe 303 is introduced into the cavity theslidable part is preferably pushed down until it abuts the portion 303d.A continuous pipe with just one aperture 301a is thus formed. Thesuction pipe can thus be used firstly as an injection lance and then asa suction pipe 303 with just a first suction nozzle 301a if the cavityis still hard or consolidated. In this way the suction pipe can beintroduced into the cavity more easily at the beginning of the suctionprocess. As soon as the cavity has been loosened by the first suctionnozzle 301a and the concentration drawn up suddenly increases, thesecond suction nozzle 301b can be formed by pulling up the part 303k. Inthis way the first suction nozzle 301a is simultaneously opened, throughwhich further the main volume of the drawn up suspension enters into thesuction pipe.

The preferred embodiment of the suction pipe is shown in FIG. 5 andditfers from the suction pipe 303 by the facts that a ring 415 having acentral aperture in which the pipe part 4031: just slidably fits, isarranged above the basket 414, the pipe part 403d is shortened at itstop and the pipe part 403!) is lengthened at its lower end.

The suction pipe again is provided with two first nozzles, the one 401aof which is positioned in the lower end of the pipe part 403d and theother 40112 of which is positioned like an annular gap between the upperend of the pipe part 403d and the ring 415. This suction pipe can be putin the cavity even more easy. During that operation first the slidablepipe part 403k is slided downwards until it abuts the pipe part 403d andthe suction pipe is alternatively used as an injection lance and as asuction pipe having only one first nozzle 401a as long as the cavity infront of the nozzle is still consolidated. As soon as the cavity infront of this nozzle is loosened and the concentration of spoil drawn upis large, the pipe part 403b is lifted up to such a height, that itslower end remains below the ring 415. The pipe part 4031) is held inthis position until the cavity surrounding the basket is loosened. Whena too large spoil concentration threatens to be drawn up, the pipe 40317is lifted to clear the ring 415 and allow water to enter the lower endof pipe 40312.

During carrying out the method according to the invention by means of asuction dredger installation according to FIGS. 4 and 5, the water inletis adjusted at such a height above the first nozzle 30111 or 401arespectively that the pressure at the inside of the spoil inlets is notmuch lower than on the outside. This prevents any clogging of any of thespoil inlets or at least greatly reduces the chance of disturbingclogging. Since the end of the suction pipe is inserted into the cavityand moved along in good time, the spoil of the cavity is loosened byundermining and prepared as a readily dredged suspension having a highspoil concentration. The suction at the spoil inlet, which isprincipally the cause of clogging in conventional methods, can be smallin the method of the invention, firstly because the suction nozzle iscontinuously kept in a suspension having a high spoil concentrationinstead of in front of a cavity which has to be worked loose, andsecondly because a small part of the total flow of the suspension is fedthrough the spoil inlets. The water, which forms the greater part of theflow through the pump, does not enter the suction pipe via thesuspension inlets. As soon as a large object covers a particular spoilinlet of the embodiments of FIGS. 4 and 5, turbulent flow occurs as aresult of the spoil currents through the other spoil inlets and as aresult of the movements of the suction pipe which take placeperiodically or continuously, and these turbulent currents have anopposite direction at the covered inlet; in other words, a pressuredifference occurs over the covered inlet and is opposed to the smallpressure difference normally prevailing over such inlet and evenoutweighs such pressure difference. Consequently nearly every object isdetached from the inlet in question and drops behind the pipe.

For removing large objects possibly sticking in the spoil inlets, thepipe part 3031) or 4013b may be lifted periodically so that every timesuch lifting occurs the suction at the spoil inlets is decreased.

Lifting the pipe part 303b or 40312 from the operational position willcause a reversal of spoil flow and thus removes said sticking objectsfrom the spoil inlets.

If necessary, a cutter may be provided at the end of the suction pipe toloosen the hard cavity immediately in front of the first suction nozzle.The meshes of the basket 314 or 414 respectively are preferablyconstructed in the form of tubes which are connected to a water pump andwhich at the end adjacent the hard cavity are provided with exitapertures for water under pressure. If this basket strikes against thehard cavity the meshes make their own path therethrough and thusundermine the sand and clay above the basket.

What is claimed is:

1. A method of suction dredging sand which comprises the steps of:

inserting a suction pipe into a body of sand below the level of thebottom of a body of water so that a column of sand tends to form in saidpipe due to the static head on the sand,

introducing water from a source above said bottom into said suctionpipe,

commingling said Water with said column of sand at a selected pointalong the length of said suction pipe,

subjecting said suction pipe to a source of suction to withdraw waterand sand through said pipe,

and essentially adjusting the level of said selected point to a pointadjacent that level to which said column will rise in the suction pipedue to the static head on the sand.

2. The method of suction dredging particulate material below the bottomof a body of water, which comprises the steps of:

forming a column of high concentration material by inserting a suctionpipe into a body of the material below the level of the bottom of a bodyof water, said column extending upwardly from the lower end of saidsuction pipe,

subjecting the upper end of the suction pipe to a source of suction towithdraw the particulate material through the lower end of the pipe,

introducing water into said suction pipe at a selected point along thelength of the suction pipe which is spaced above the lower end thereofand commingling water with the particulate material at said selectedpoint,

and adjusting the location of said selected point with respect to thelower end of the pipe to maintain the concentration of particulatematerial in the particulate material-water mixture above said selectedpoint within predetermined limits.

3. The method according to claim 2 wherein the concentration ofparticulate material in the mixture withdrawn is maintained within therange of about 10% to about 25%.

4. The method according to claim 2 including the steps of measuring theconcentration of particulate material in the mixture being withdrawnthrough the pipe above said point at which the particulate material andwater are commingled, and controlling the location of said point inresponse to the concentration measured.

5. A suction dredger installation comprising a pump and a suction pipehaving an upper end connected to said pump and which has at least onefirst nozzle for spoil at its lower end and at least one second nozzlemainly for water between the pump and said. lower end, and means foradjusting the level of said second nozzle independently of the levels ofsaid upper end of the suction pipe and of said first nozzle to vary thedistance between the two nozzles;

said suction pipe comprising inner and outer pipe sections, said outersection having an open lower end forming said first nozzle and saidinner section having an open lower end forming said second nozzle withthe surrounding wall of said outer section, said means being connectedto said inner section to axially shift same within said outer section;

the lower end of said outer section being provided with an annular discpresenting an opening for receiving said inner section whereby suchopening is closed; and

a sleeve carried at the lower end of said outer section beyond theopening of the latter, said sleeve being aligned with said inner sectionfor engagement by the lower end thereof.

6. A suction dredger installation comprising, in combination:

a suction pump adapted efiiciently to induct and discharge fluidsuspensions of sand in water having selected values of sandconcentration therein, and having an inlet for inducting suchsuspensions;

suction pipe means connected to said inlet and having an open lower endadapted to be inserted deeply into a body of sand below the level of thebottom of a body of water so that a first column of sand and water tendsto form in said suction pipe means due to the static head on the sand,in which the concentration of sand in said first column is much greaterthan said selected values;

7 means for introducing water into said suction pipe means at a selectedpoint along the length of said suction pipe means and for comminglingwater with said first column of sand and water to form a second columnof water and sand above said first column which extends therefrom tosaid inlet; and means for adjusting the level of said selected pointwith respect to said lower end of the suction pipe means to a pointadjacent that level to which said first column will rise in the suctionpipe means due to the static head on the sand whereby the concentrationof sand in said second column is within said selected values. 7. Thesuction dredger installation according to claim 6 including means formeasuring the concentration of sand in said second column, said meansfor adjusting being controlled bysaid means for measuring.

8. The suction dredger installation according to claim 6 wherein saidsuction pipe means comprises a first pipe directly connected to saidinlet of the pump, an outer jacket surrounding said first pipe andhaving an opening above said first column for admitting water thereinto,and a second pipe slidably engaging said first pipe; and wherein saidmeans for adjusting comprises an actuator for moving said second piperelative to said first pipe.

9. The suction dredger installation according to claim 8 wherein saidfirst pipe has a fixed lower end below which said jacket extends topresent an open lower end thereat, and said second pipe is of a lengthto extend between said lower end of said first pipe and said lower endof the suction pipe means.

10. The suction dredger installation according to claim 9 including anozzle fixed at and projecting from said lower end of said suction pipemeans, said second pipe being aligned with said nozzle for engagementtherewith so that said jacket may be isolated from said first pipe.

11. The suction dredger installation accordingto claim 6 wherein saidsuction pipe means comprises a first pipe directly conected to saidinlet of the pump, and an outer jacket surrounding said first pipe andhaving an opening above said first column for admitting water thereinto,and wherein said means for introducing water comprises opening meansalong the length of said first pipe.

References Cited UNITED STATES PATENTS 780,027 1/1905 Edwards et al30258 X 850,639 4/1907 Gebhardt 30258 934,031 9/1909 Askew 37582,125,740 8/1938 Schacht 37-62 2,661,550 12/1953 Graham 3758 2,768,52910/1956 Hagler, Sr 73438 3,111,778 11/1963 Fonnesbeck 3758 3,153,29010/1964 Saito 37--62 FOREIGN PATENTS 77,447 5/1933 Norway 30258 111,17311/1917 Great Britain 30258 274,198 5/1914 Germany 30258 459,568 9/ 1949Canada 37-58 697,492 10/ 1940 Germany 37-63 1,167,263 4/1964 Germany30258 ROBERT E. PULFREY, Primary Examiner C. D. CROWDER, AssistantExaminer U.S. Cl. X.R.

